The present invention relates to a receiver and a method for gain control, and for example, to a receiver and a method for gain control for removing an interference wave component.
Superheterodyne receivers for converting a reception signal into an intermediate frequency signal and performing signal processing on the intermediate frequency signal are widely used. In general, a signal having a frequency which is a target frequency for reception (a desired wave) and a signal having an unnecessary frequency (an interference wave) are mixed in a signal that is input to a receiver. Therefore, various techniques for reducing an influence of the interference wave and improving reception performance have been developed. A technique for reducing the influence of the interference wave shall be explained below.
Japanese Unexamined Patent Application Publication No. 2011-87034 (Patent literature 1) discloses a reception circuit that can achieve a high interference wave suppression ratio in a case of receiving an interference wave having a frequency close to a desired wave, which has a target frequency for reception, and also in a case of receiving an interference wave having a frequency distant from the desired wave. The reception circuit includes an AGC loop, a filter group having an active filter that is provided in a stage subsequent to the AGC loop and a difference power detection unit for detecting an existence of the interference wave having a frequency close to the desired wave by detecting a differential voltage between an intermediate node and an output node of the filter group. The reception circuit further includes a switching circuit for switching convergence power of the AGC loop to reduce the convergence power of the AGC loop when the difference power detection unit detects the interference wave that is adjacent to the desired wave.
Japanese Unexamined Patent Application Publication No. 2011-211539 (Patent literature 2) discloses a receiver that has realized an improvement in an interference wave suppression ratio in a manner similar to Patent literature 1. The receiver has a configuration in which an evaluation is performed on whether or not an interference wave received together with a desired wave is an interference wave adjacent to the desired wave, and control is performed on an AGC loop according to the evaluation.
Japanese Unexamined Patent Application Publication No. 2009-16912 (Patent literature 3) discloses a gain control circuit for detecting an existence of a disturbing wave (an interference wave), and when the disturbing wave is detected, the gain control circuit detects TOP (a setting level for determining a gain which will be set to an amplifier) that can achieve a favorable BER (Bit Error Rate) while changing the TOP.